1. Field of the Invention
The present invention relates to a method of screen printing a pattern on a target object, and more particularly to a method of screen printing a printed pattern on a substrate utilizing a removable barrier layer to ensure proper alignment of the printed pattern.
2. Description of the Related Art
The manufacture of substrates such as printed circuit boards, Integrated Circuit (IC) chips or wafers requires the screen printing of patterns of symbols, passive elements, wiring portions, or the like on the surface of the substrate. The alignment of the pattern on the substrate is critical, as a misaligned pattern can result in an unusable substrate due to misaligned symbols or an inoperative circuit due to misaligned wiring portions.
In screen printing, a silk screen of the pattern desired to be transferred to the substrate is aligned with and secured to the substrate with an epoxy adhesive. However, this has a disadvantage in that once the pattern is placed on and adhered to the substrate, it may not be removed without causing damage to the substrate itself. Since the proper alignment of the pattern may be crucial to the proper operation of the substrate in the end circuit, the only recourse for a substrate having a misaligned pattern is to reject the entire substrate, as there is no way to remove the misaligned pattern to rework the screen printing without damaging the substrate. This results in a waste of materials, as an entire substrate must be rejected based upon a misaligned print pattern.
FIG. 1 shows an example of a properly aligned solder bond pattern on a substrate. Substrate 10 may be a printed wiring board, IC chip or the like, on which it is necessary to print a solder bond pattern properly aligned with the areas 11-14 and 16-19. Assuming, for example, it is desired to print a pattern 20 consisting of eight solder bond pads 21-24 and 26-29 corresponding to areas 11-14 and 16-19 on substrate 10, the pattern 20 would be lined up with substrate 10 and applied to substrate 10 with an adhesive (not shown), such as an epoxy based adhesive or a polyimid siloxane adhesive. If the pattern 20 is properly aligned, the solder bond pads 21-24 and 26-29 will be properly aligned with areas 11-14 and 16-19 of substrate 10 as shown by the complete substrate with pattern 30.
FIG. 2 shows an example of a misaligned pattern on a substrate. Substrate 110 may be a printed wiring board, IC chip, wafer or the like, on which it is necessary to print a pattern properly aligned with the areas 111-114 and 116-119. Assuming, for example, it is desired to print a pattern 120 consisting of eight bond pads 121-124 and 126-129 corresponding to areas 111-114 and 116-119 on substrate 110, the pattern 120 would be lined up with substrate 110 and applied to substrate 110 with an adhesive (not shown), typically an epoxy based adhesive or a polyimid siloxane adhesive. If the pattern 120 is properly aligned, the bond pads 121-124 and 126-129 will be properly aligned with areas 111-114 and 116-119 of substrate 110. However, if the pattern 120 is not properly aligned, then bond pads 121-124 and 126-129 will not be properly aligned with areas 111-114 and 116-119 as shown by the complete substrate with misaligned pattern 130. In this instance, since the misaligned pattern 120 could cause improper operation of the complete substrate 130, it is necessary to remove the pattern 120 from substrate 110 and rework the substrate 110 to properly align the pattern 120. However, since the adhesive used to secure pattern 120 to substrate 110 may be partially absorbed by substrate 110, it may not be possible to remove the misaligned pattern 120 from the substrate 110 without causing damage to substrate 110. Thus, it is necessary to reject the entire complete substrate 130, resulting in a waste of material.
Thus, there exists the problem of being able to screen print a substrate in which a misaligned pattern can be removed without causing damage to the substrate.